In recent years, the needs for the characteristics of a silver halide light-sensitive material for photographic use have been more exacting. There have been higher level demands for the photographic characteristics such as sensitivity, fog and granularity and for the preservability. Recently, in particular, with the popularization of a compact zoom camera and a film attached with a camera mechanism that is so-called a camera with a lens, it has become inevitable for a photographic light-sensitive material to make a sensitization higher. Besides, a silver halide light-sensitive material has been preserved in various environments and used under various conditions. Therefore, the storage stability of photographic characteristics thereof have also strongly been required.
For satisfying the above-mentioned requirements, various techniques for improving a silver halide light-sensitive material have been developed. The highly sensitizing techniques applicable to a silver halide emulsion include, for example, those for an internally high iodide-containing core/shell type silver halide grain typified by a multiple-layer structured grain, such as those disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP OPI Publication) No. 60-14331/1985. When silver iodide is contained in a silver halide grain, a photoelectron is inhibited from recombination by trapping a positive hole produced when the grain is made photosensitive, so that a latent-image forming efficiency can be improved. However, when increasing the silver iodide content, chemical sensitization nuclei produced by applying a chemical sensitization to the silver halide grain is dispersed, so that the latent-image forming efficiency may be lowered and, in addition, that the development activity of the silver halide grain may also be impaired. For solving the above-mentioned contradictory problems, the above-described technique intends to make compatible both of an efficient positive hole trapping function and a development activity by covering a core having a relatively high silver iodide content with a shell having a relatively low silver iodide content.
In an ordinary photographic light-sensitive material, a spectral sensitizing dye is adsorbed to the surface of the silver halide grain so as to give a spectral absorption property to the grain. However, when an adsorption of a spectral sensitizing dye to a silver halide grain is relatively weak, there may be some instances where a dye adsorbed to the surface of silver halide grains may be desorbed in the course of preserving the light-sensitive material, so that the sensitivity may be lowered; (this phenomenon may be remarkable particularly under the conditions of a high humidity and a high temperature.) Generally, the more a silver iodide content of the surface of a grain is increased, the more an adsorption of a sensitizing dye to a silver halide grain is also increased. It can, therefore, be expected that a preservability can be improved and a high sensitivity can also be obtained by increasing a silver iodide content of the surface of a silver halide grain.
As for a technique for intending the same as above, JP OPI Publication No. 5-75096/1993 discloses a silver halide photographic light-sensitive material comprising an internally high iodide-containing core/shell type silver halide grain having the surface portion where the silver iodide content is higher than that in the shell section and is also not less than 5 mol %. With the above-mentioned technique, however, it has been unable to solve such a problem that an initial developability is lowered and chemical sensitizing nuclei are dispersed. On the other hand, as a technique capable of realizing the improvement of a dye adsorbability and, at the same time, solving the problems of lowering a developability and dispersing chemical sensitizing nuclei, JP OPI Publication No. 3-237451/1991 discloses a silver halide photographic light-sensitive material comprising a silver halide grain comprising a portion ranged from an atomic layer constituting the uppermost surface of the grain to the fifth atomic layer, (for example, a section from the uppermost layer to the position of 14.4.ANG. in the case of a cubic silver bromide grain), wherein the silver iodide content of the portion is relatively higher than that in the internal phase adjacent to the portion.
However, the demands for improving photographic characteristics have become more serious year by year, and a technique capable of realizing further progressed photographic characteristics has been requested.